1. Field of the Invention
The present invention relates to a spring guide and a cushion device.
2. Discussion of the Background
Vehicles such as motorcycles and buggies include cushion units to suspend their wheels. These cushion units have a function to appropriately buffer a vertical movement caused by the travel of the vehicle or the like. For example, in a case of a motorcycle, a rear wheel is supported rotatably by a swing arm provided vertically swingably to a vehicle body frame, and a cushion unit is placed between the swing arm and the vehicle body frame, thereby buffering the vertical movement of the rear wheel caused by travel. Thus, the drivability and ride quality are maintained at some levels.
As to the structure, the cushion unit includes a damper set in which an inner shaft member is fitted in a cylindrical outer shaft member slidably in the axial direction thereof, and a coil spring which has the dumper set housed therein coaxially and is disposed across the outer shaft member and the inner shaft member. As to the function, the vertical movement of the wheel caused by the travel of the vehicle is buffered by the coil spring and damped and absorbed by the damper set. Accordingly, the ride quality and so forth are maintained at some levels.
Here, the cushion unit buffers the vertical movement of the wheel by use of the extension and compression of the coil spring. Incidentally, the coil spring also receives vibrations of relatively high frequencies, such as vibrations caused by the travel over a road surface with small bumps and engine vibrations. This may cause the coil spring to resonate with the vibrations of the high frequencies and creates a situation where the vibrations of the vehicle body are affected, where the coil spring is rubbed against other components of the cushion unit, or where abnormal noises like chatter noises are generated by the vibrations of the coil spring itself. To solve this situation, various improvements have heretofore been proposed.
To briefly describe improvements proposed so far for the cushion unit, there is, for example, a structure using a relatively thick rubber cap to cover one end portion of the coil spring, thereby suppressing the vibrations. Moreover, improvements as illustrated in FIGS. 8 and 9 have been proposed as well.
A conventional cushion unit 65 shown in FIG. 8 is characterized by a structure in which a coil spring (64a, 64b) to be disposed across an outer shaft member 61 and an inner shaft member 62 is divided into two springs.
Specifically, in the structure shown in FIG. 8, a cylindrical spring seat 66 covering the outer shaft member 61 is provided to the outer shaft member 61 slidably in the axial direction thereof. A coil spring 64a is disposed between a flange 66a provided to the spring seat 66 and a flange 61a at the outer shaft member side. In addition, another coil spring 64b is disposed between the flange 66a and a flange 62a at the inner shaft member side. According to this structure of the cushion unit 65, the coil springs 64a and 64b, which differ from each other in resonance point, are jointed with the spring seat 66 therebetween, and thus the coil springs 64a and 64b interfere with each other. Consequently, the aforementioned resonance is suppressed.
Another conventional cushion unit 40 shown in FIG. 9 is one disclosed in Japanese Patent Application Publication No. 2005-282585. In its structure, a cylindrical spring guide 57 covering an outer shaft member 51 is provided to the outer shaft member 51 slidably in the axial direction thereof, and a coil spring 56 is disposed between a flange 59 of the spring guide 57 and a flange 52a at an inner shaft member side.
Moreover, in the structure, the cylindrical spring guide 57 having slits 58a is provided between the outer shaft member 51 of a dumper set 53 and the coil spring 56. Furthermore, the spring guide 57 is biased in a widening direction by an elastic ring 63 provided to a leading end side thereof (near the center of the cushion unit) so that the diameter of the seat would become larger. Thus, the spring guide 57 is aggressively brought into contact with the coil spring 56 that may vibrate due to the vibrations caused by travelling of the vehicle, or the like. Accordingly, the vibrations of the coil spring 56 are suppressed.
The cushion unit 40 as above only requires the spring guide 57 to be placed inward of the coil spring 56. This prevents the cushion unit from increasing in size and also allows the cushion unit 40 to be assembled without a cumbersome and complicated work.
Meanwhile, although the invention described in Japanese Patent Application Publication No. 2005-282585 improves the aforementioned conventional problems relatively well, there still remains room for improvement regarding noises produced when the spring guide 57 and components placed inward thereof hit each other. Moreover, the spring guide 57 disclosed in Japanese Patent Application Publication No. 2005-282585 exhibits its vibration suppressing performance by use of the combined structure with the elastic ring 62 attached to the seat itself as described above. The shape of the seat itself is therefore likely to be complicated. Thus, the assemblability remains as a problem to be solved.